A deterministic approach for integrating an emitter in a nanocavity with subwavelength light confinement

TL;DR

The work addresses deterministic, strongly coupled light–matter interfaces in solid-state nanophotonics by embedding a lithographically defined buried heterostructure emitter inside a subwavelength bowtie cavity. It introduces a generalized mode volume V_Gamma based on the emitter’s finite spatial extent and a confinement-factor framework, enabling accurate g predictions beyond the dipole approximation. Through full-wave and Schrödinger simulations, topology optimization, and InP/InGaAsP modeling, it predicts coupling strengths of 0.4–0.7 meV for 50–10 nm gaps and demonstrates a geometry crossover from bowtie to slit cavities that optimizes emitter–field overlap. The approach offers a practical pathway to scalable, deterministic strong coupling with realistic fabrication and surface-passivation considerations, potentially enabling near-term solid-state quantum photonic devices.

Abstract

We introduce a novel light-matter interface that integrates a nanoscale buried heterostructure emitter into a dielectric bowtie cavity, co-localising the optical hotspot and the electronic wavefunction. This platform enables strong light-matter interaction through deep subwavelength confinement while remaining compatible with scalable fabrication. We show that in this regime an explicit treatment of the emitter's spatial extent is required, and that a confinement-factor approximation more accurately predicts the coupling, revealing design rules inaccessible to dipole-based metrics. For an InP/InGaAsP system, we predict coupling strengths of 0.4-0.7 meV for gap sizes of 50-10 nm, establishing the buried heterostructure-bowtie architecture as a practical route to deterministic strong coupling in solid-state nanophotonics.

Figures (5)

• Figure 1: Proposed bowtie–buried heterostructure (BH) cavity system. (a): Three-dimensional rendering of the bowtie nanobeam cavity within a one-dimensional photonic crystal. (b): Enlarged cross-sectional view showing the etched BH within the bowtie gap, defining the key parameters $b_g$ (gap size) and $l_{BH}$ (lateral BH size). (c): Calculated optical field amplitude $n^2|E|^2$ and (d) electronic envelope probability density illustrating their spatial overlap.
• Figure 2: (a): Calculated coupling strength $\hbar g$ as a function of bowtie gap size $b_g$ for a buried heterostructure of size $l_{BH}=50~\text{nm}$. Three approaches are compared: the full wavefunction-based model, Eq. \ref{['eq:g_general']}, the point-dipole approximation, Eq. \ref{['eq:g_dipole']}, and the confinement-factor-based model Eq. \ref{['eq:g_conf']}. Inset: Sketch of the lithographic light matter interface with the bowtie gap $b_g$ and BH size $l_{BH}$ defined. The initial BH size, before etching, is illustrated by the translucent dashed rectangle. (b): The mode volumes obtained from the dipole and confinement factor approaches are compared. The conventional dipole mode volume $V_c$ is obtained from the field intensity at the central point of the cavity with $l_{BH}=50$nm.
• Figure 3: (a): The confinement factor derived mode volume of the topology optimised cavities compared to a previously studied H1 cavity, for different emitter sizes. (b): The optical field $n^2 |E|^2$ are plotted in the colourmap for the H1 cavity, where two BH sizes are indicated with the coloured circles and corresponding colours for the data points in plot (a). The topology-optimised geometries and field distributions are shown in (c) for a BH with a radius of $5$ nm, similarly in (d) for $25$ nm, and (e) for $150$ nm.
• Figure 4: Calculated electron probability density $|\psi(x,y)|^2$ of the lowest‑energy eigenstate, in the central plane of the bowtie cavity for buried heterostructure sizes of $l_{BH}=20$ nm (left) and $l_{BH}=30$ nm (right) for a gap size of $b_g=$ 10 nm.
• Figure 5: Coupling strength $\hbar g$ as a function of inverse gap size, for emitter sizes scaled such that $b_g = l_{BH}$. The scaling relation in eq. \ref{['eq:scalinglaw']} is represented by the orange solid line. The square marker shows the experimental result from Ohta et al. Ohta2011 for a stochastically grown quantum dot in a conventional nanobeam cavity without a bowtie. Here, the value of $b_g$ represents the distance between the two central holes.